Testing steel

I've acquired three 50 gallon steel drums which I think were used in hot water systems.

I need to know whether or not they are stainless steel (as opposed to non-stainless). How can I test them?

Stratis.

Not a definitive test, but SS is only slightly attracted by a magnet. Ed H. will probably be around shortly to give an authoritative answer.

Color alone is a good indicator. Stainless drums are generally not painted and have a somewhat frosty silvery appearance. They are also not magnet, although if they're cold worked enough they can be slightly so. Some of them, such as those used for nitric acid, often have steel bands located at roughly one third of their lengths from each end, so if you check with a magnet, be certain you apply it to the drum, not any hardware attached to them. They're very costly if purchased new, in the hundreds of dollars as I understand it. I recall that the deposit for the one I used to get containing nitric was $400.

Harold

A magnet will not stick to food grade stainless. Note that there are lots of corrosion resistant steel alloys, some are magnetic.

Which is typically either 304 or 316 stainless. Both are lightly magnetic when work hardened, like in having been heavily spun and not annealed.

Harold

I know that after machining SS the heat creates a martensitic structure that does not allow for magnetic alignment. so I believe that once heated and immediately quenched ( maybe with compressed air) SS will have no attraction to magnet. Regular carbon steel will still maintain some magnetism.

Open to correction

I'm having a little trouble with the idea that machining creates enough heat to make such a change. Transformation takes place at quite high temperature, typically red heat.

Yep, but that's not the point. One isn't checking to see if the drum is a magnet. The inspection procedure is to determine if the drum is

*magnetic*, which would sort out steel from stainless. Dead annealed, a steel drum is still very magnetic. A stainless drum (300 series stainless) would not be.

Harold

AFAIK, ferrite is magnetic and martensite will retain magnetism (hence magnets made of hard steel). If austenitic stainless does indeed form martensite on work hardening, that would explain the increase in magnetism.

AFAIK, heating any 300 series stainless, quenched or not, will only effectively anneal it, as with mild steel (correct me if I'm wrong).

Tim

When you work-harden 300 Series stainless, some austenite is converted to martensite. This is what makes work-hardened 300 Series slightly magnetic.

There are special, modified versions of some common 300 Series stainess steels that are formulated specifically to prevent them from becoming magnetic upon work-hardening. These are intended primarily for wire-drawing, where the reduction in section is extreme and the resulting magnetism can be a problem in some applications. These special grades get their non-magnetic properties from very small additions of copper to the alloy.

Heat treating 300 Series stainless, in general, will do nothing but anneal it. There are some minor exceptions that you can read about with a Google search. You won't get significant hardening with *any* 300 Series grade from heat treating, however.

The easiest way to tell if a steel drum is stainless is by testing it with a magnet. Any carbon steel and any common alloy steel that might be used for making drums will be very magnetic. No stainless used to make a drum will be more than very slightly magnetic. There's no mistaking the difference.

-- Ed Huntress

Take a grinder or sanding disk and sand to bare metal. Put water on the ground surface and see if it rusts. You might have to wait for some time. If no rusting for a couple days then use a magnet to check for magnetic attraction. If it is a 300 series stainless it will not be attracted to the steel.

What makes you think they are stainless steel?